132 



NOKTH-CAROLINA GEOLOGICAL SURVEY. 



CHAPTER XI. 



(lay. Characteristics of a good clay. Composition of fine clays. Com- 

 position of a clay upon Bogue Sound. 



99. Clay, though rarely, if ever, a constituent part *of a 

 vegetable, is still an important substance in matters pertain- 

 ing to agriculture. It is one of the most important substances 

 in construction. It is also employed largely in the manufac- 

 ture of articles indispensable in the economy of the house- 

 hold, and is the principle material employed in the draining 

 tile. 



Clays differ widely from each other; some are fusible; 

 others are very refractory in the fire, or scarcely fusible by 

 the highest heat of a furnace. For certain purposes, the re- 

 fractory clays are indispensable. For lining stoves and fur- 

 naces, this property should exist in an eminent degree. For 

 household utensils, it is not necessary the clay should be 

 highly refractory in the fire. As different properties are re- 

 quired for the different uses to which clay is to be put, it is 

 desirable that the adaptedness of clay for a special purpose 

 should be determined by methods which are within the reach 

 of every intelligent individual ; at least that good clay may 

 he determined by some simple and easy experiment. 



In the first place, good clay is homogeneous ; it is free from 

 lumps, stones and other foreign matter. In the second place, 

 it should have an unctuous feel ; this property implies tena- 

 city, and an ability to mould readily and retain forms and 

 shapes which is given to it by 'working. 



In the third place it should contain sand. Too much sand 

 destroys cohesion, but a certain proportion of sand imparts to 

 clay an ability to dry or season. Bricks, tiles and all utensils 

 must dry through before they can be burned, else they will 

 crack when exposed to the heat of the kiln. Excess of sand 

 renders moulded clay weak and unfit for handling; its tena- 



